Electroconductive polymer composites for use in secondary batteries as positive electrode active materials

ABSTRACT

An electroconductive polymer composite for use in secondary batteries as positive electrode active materials is disclosed. It includes 10-99 weight percent of a conjugated electroconductive polymer, such as polyaniline, and 90-1 weight percent of polymeric electrolyte. The latter is composed of 10-90 weight percent of an ionic salt, such as LiClO 4 , and 90-10 weight percent of a polymer which can form an electrolyte material with the ionic salt. The polymer, for example, can be polyvinyl alcohol or polyalkylene oxide. A method of using the electroconductive polymer composite to prepare the positive electrode of secondary batteries is also disclosed. It includes the steps of dissolving the above three components in an appropriate solvent (such as 1-methyl-2-pyrrolidinone), casting the resulting solution on an appropriate metallic grid or plate (such as nickel, aluminum or platinum) and removing the solvent therein to form a film which adheres to the metal grid or plate, in which the film is a positive electrode active material and the metallic grid or plate is a current collector. This invention also discloses a non-aqueous secondary battery which uses such positive electrode.

This is a divisional application of application Ser. No. 08/410,434,filed Mar. 3, 1995, now U.S. Pat. No. 5,667,913.

FIELD OF THE INVENTION

The present invention relates to a non-aqueous secondary battery,particularly a non-aqueous secondary battery which compriseselectroconductive polymer composites used as positive electrode activematerials.

BACKGROUND OF THE INVENTION

On applications for organic secondary batteries, in 1967 M. Jozefowiczet al. (French Pat. N.P. 95630) innovated in using polyaniline (PAn) asthe battery electrode and expanded the development of the organicbattery. In 1981, A. G. MacDiarmid et al. (J. Chem. Soc. Chem. Commun.,(1981) 317) successfully used electrochemically doped polyacetylene (PA)as the electrode of an organic secondary battery. And E. M. Genies etal. (Mol. Cryst. Liq. Cryst., 121 (1985) 181; Mol. Cryst. Liq. Cryst.,121 (1985) 195) used p-type doped polyaniline as the positive electrodeand lithium as the negative electrode to form an organic secondarybattery with high energy density and cycle life. Goto et al. (J. PowerSources, 20 (1987) 243) found that among the secondary batteries withPAn, PA, polypyrroles (PPy), polythiophene (PT), etc. as electrodes, theone with PAn has the best performance. It has the advantages of highenergy density, power density, capacity efficiency, long cycle life andlow self-discharge.

So far, organic secondary batteries, which use polyaniline as thebattery plate, can be classified into three major categories. The firstgroup are secondary batteries containing aqueous electrolyte A. G.MacDiarmid et al., Mol. Cryst. Liq. Cryst., 121 (1985) 187; A. Kitani,M. Kaya, and S. Sasaki, J. Electrochem. Soc., 133 (1986) 1069; N. L. D.Somasiri et al., J. Applied Electrochemistry, 18 (1988) 92; A. G.MacDiarmid et al., U.S. Pat. No. 5,023,149 (1991); F. Trinidad et al.,J. Electrochem. Soc., 138 (1991) 3186!. The second group are organicsecondary batteries containing non-aqueous electrolyte A. Kitani et al.,Bull. Chem. Soc. Japan, 57 (1984) 2254; E. M. Genies et al., SyntheticMetals, 18 (1987) 631; F. Goto et al., Synthetic Metals, 18 (1987) 365;Ricoh Co. U.S. Pat. No. 5,037,713 (1991)!. The third group are organicsecondary batteries containing solid polymeric electrolyte Hydro-Quebec,U.S. Pat. No. 4,758,483; C. Arrbizzani et al., Synth. Met., 28 (1989)C663; Li Changzhi et al., J. Power Sources, 39 (1992) 255; T. Ohsawa etal. (Ricoh Corp.) Synthetic Metals, 41 (1991) 3021!. In non-aqueousmedia, usually lithium was used as the negative electrode because of itshighest oxidation potential, and light weight and easy for extension. Itnot only provides an increased open circuit voltage (Voc), but also anelevated unit mass charge capacity. When aqueous solution is used as theelectrolyte, the negative electrode material should be a metal with alower oxidation potential (such as Zn, Al). This makes the open circuitvoltage (1.0 V) and the energy density (100 Whr/kg) lower than those ofthe non-aqueous battery. Therefore, organic secondary batteries withnon-aqueous electrolyte are of more practical value. The electrolyte canalso be a solid. it is composed of polyethylene oxide (PEO) or itscopolymer with salt. It provides the advantages of higher stability athigh voltage and reduced demand in electrolyte quantity. However, it isof practical use only at temperatures above 60° C. (M. Duval et al.(Hydro-Quebec), Makromol. Chem., Makromol. Symp., 24 (1989) 151).

The synthesis methods of polyaniline include the chemical method J.Langer, Solid State Commun., 26 (1978) 839; M. Jozfowicz, J. PolymerSci., C22 (1969) 1187; J. P. Travers et al. Mol. Cryst. Liq. Cryst.,121(1985)195) and the electrochemical method (D. M. Mohilner et al., J.Am. Chem. Soc., 84 (1962) 3618; E. M. Genies et al., Mol. Cryst. Liq.Cryst., 121 (1985) 181!. The doped polyaniline powder made by thechemical method can not be dissolved in common organic solvents, whichlimits its practical applications. In 1987, A. G. MacDiarmid et alSynth. Met., 21 (1987) 181! first found that de-doped polyaniline powdercan be dissolved in NMP (1-methyl-2-pyrrolidinone) and then can be castinto film. NMP is the only known organic solvent that can completelydissolve polyaniline. In 1991 R. L. Elsenbaumer(U.S. Pat. No. 5,006,278)proposed that the polyaniline powder can be dispersed in nitromethane inthe presence of ferric chloride, in which the polyaniline issimultaneously doped and dissolved. In 1990, Bridgestone Co. (U.S. Pat.No. 5,066,556 (1991); U.S. Pat. No. 4,957,833 (1990)) used thepolyaniline deposited on a current collector, which was synthesizedelectrochemically, together with lithium (or lithium alloy) as counterelectrode to compose of a button battery having a discharge capacity of80 Ahr/kg. The drawback of this method is that to produce an organicsecondary battery with a large electrode area is difficult. RecentlyRicoh Co. U.S. Pat. No. 4,999,263 (1991); U.S. Pat. No. 4,948,685(1990)! has used the electrochemical method to synthesize a polyanilinefilm of 0.05 mm thick on a porous metallic film as working electrode andto produce a film battery with outside dimensions of 50 mm long, 50 mmwide and 0.9 mm thick. The battery has an energy density of 326 Whr/kg.However, the polyaniline film is brittle and can not be wound. So far,the known methods to produce a polyaniline electrode in a polyanilinesecondary electrode include the following:

(1) Using the chemical method to synthesize polyaniline, mixing thedoped polyaniline powder with carbon black and binder and casting theresulting mixture into a film, and pressing the film to adhere on ametallic grid. The metallic grid here is used as a current collector (A.G. MacDiarmid et al., Synthetic Metals, 18(1987)393; E. M. Genies etal., J. Applied Electrochemistry, 18 (1988) 751; M. Mizumoto et al.,Synthetic Metals, 28(1989)C639).

(2) Using the electrochemical method to synthesize polyaniline film on ametal substrate. The metal substrate here also serves as a currentcollector. The polyaniline film synthesized by the electrochemicalmethod has a porous fibrilar structure similar to polyacetylene, and hasa large specific area. The film has a large contact area with theelectrolyte solution, allowing a high diffusion rate of the chargecarriers into the film so as to increase the mass charge capacity of theproduced battery (F. Goto et al., J. Power Sources, 20 (1987)243; S.Tangnshi et al., J. Power Sources, 20(1987)249; E. M. Genies et al.,Synthetic metals, 29(1989)C647; Susumu Yonezawa et al., J. Electrochem.Soc., 140(1993)629; Bridgestone Corp. U.S. Pat. No. 5,066,556 (1991);U.S. Pat. No. 4,906,538 (1990); U.S. Pat. No. 4,939,050 (1990); RicohCorp. U.S. Pat. No. 4,999,263 (1991); U.S. Pat. No. 4,948,685 (1990)).

There are many drawbacks in the two methods for producing polyanilineelectrodes as described below:

(1) Using polyaniline synthesized by the chemical method to produce theelectrode:

1. The polyaniline synthesized by the chemical method is in powder formand requires pressing to form a film. The polyaniline electrode soproduced has a weak mechanical strength and is easy to crack understress.

2. Since the polyaniline powders are adhered together through the use ofpolymeric binder and then pressed with the current collector to give aworking electrode, the contacts among the polyaniline powders andbetween the polyaniline and current collector are poor. Thus, theinternal resistance of the electrode is increased and the batteryperformance is decreased.

3. The polyaniline synthesized by the chemical method has a surfacemorphology more compact than that synthesized by the electrochemicalmethod. The contact area of the electrode with the electrolyte solutionis therefore smaller.

During the process of charging and discharging, the ion diffusionresistance is greater, therefore, the battery performance is lower.

4. The method can not produce an electrode of large area; therefore, itspractical value is limited.

(2) Using polyaniline synthesized by the electrochemical method toproduce the electrode plate.

1. The polyaniline synthesized by the electrochemical method isdifficult to be used for preparing a battery electrode with large area.Therefore, currently there is only button type battery available in themarket Bridgestone Corp. U.S. Pat. No. 4,957,833 (1990)!.

2. The process for producing polyaniline by the electrochemical methodis more complicated than that of the chemical method.

3. The polyaniline film produced by the electrochemical method isbrittle and is easy to be broken by external force.

Therefore, to prepare a wound-type battery is impossible.

The main objective of this invention is to provide electroconductivepolymer composites for use in secondary batteries as positive electrodeactive materials. The composites have characteristics includingexcellent mechanical properties, conductivity, and large specificcontact area between the electroconductive polymer and the electrolyte.

Another objective of this invention is to provide a positive electrodefor a secondary battery without the drawbacks specified above.

Still another objective of this invention is to provide a non-aqueoussecondary battery which has high open-circuit-voltage (Voc), high energydensity, high charge capacity, and good stability of charge capacity.

SUMMARY OF THE INVENTION

In order to achieve the above objectives, an electroconductive polymercomposite is prepared according to the invention which comprises: 10-99weight percent of a conjugated electroconductive polymer and 90-1 weightpercent of ionized polymeric electrolyte. The later comprises 10-90weight percent of an ionic salt and 90-10 weight percent of a polymericmaterial (hereinafter referred to as the ionizable polymer), which canform an electrolyte material with the ionic salt.

Preferably, the content (weight) of the conjugated electroconductivepolymer in the electroconductive polymer composite is 1-5 times that ofthe ionizable polymer. And the content (weight) of the ionic salt islower than the content of the ionizable polymer.

In the electroconductive polymer composite of this invention, the ionicsalt and the ionizable polymer form an ionized polymeric electrolyte.And since the ionizable polymer and the conjugated electroconductivepolymer are immiscible to each other, the so formed ionized polymericelectrolyte is dispersed in the conjugated electroconductive polymerhaving particle diameters of about 1 to 3 micrometer. Therefore, theconjugated electroconductive polymer and the ionized polymericelectrolyte have a large contact area. Alternatively, the ionizablepolymer can also present as a block of the block copolymer with theconjugated electroconductive polymer. In the electroconductive polymercomposite of this invention, the conjugated electroconductive polymercan store energy and the ionizable polymer provides ductility and alsoserves as a reservoir for the ionic salt (or electrolyte). Therefore,when the electroconductive polymer composites of this invention are usedin secondary batteries as positive electrode, the electroconductivepolymer and the electrolytes of the secondary batteries have a largespecific contact area. Therefore, the ion flow rate is greatly increasedduring the process of battery charging and discharging. Furthermore, theductility provided by the ionizable polymer enables theelectroconductive polymer composites of this invention to be processedinto a large area flexible film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an organic secondary battery structure,in which 10 is a polyaniline film, 11 is a current collector, 12 is anon-aqueous electrolyte, 13 is lithium and 14 is a separator.

FIG. 2 is a diagram showing the potential of tenth charge/dischargecycle vs. charge/discharge time of a Li | 1.0M LiClO₄ -PC |PAn/PVA/LiClO₄ battery.

FIG. 3 is a diagram showing open circuit potential (Voc) vs. time ofthree different batteries, in which the positive electrode activematerials of the three different batteries respectively arePAn/PVA/LiClO₄ (---), PAn/PVA(...), and PAn(------).

FIG. 4 is a diagram showing the discharge capacity vs. charge/dischargecycles of four different batteries, in which the positive electrodeactive materials of the four different batteries respectively arePAn(-▪-) and PAn/PVA/LiClO₄ of weight ratios of 3:1:0.6(-♦-) 1:1:0.6(-▴-), and 2:1:0.5(-□-).

FIG. 5 is a diagram showing (a) SEM micrograph (magnification by 5000times) of the PAn film cast from the NMP solution of PAn synthesized bythe chemical method and (b) SEM micrograph (magnification by 5000 times)of PAn/PVA/LiClO₄ composite film with the weight ratio 2:1:0.6.

FIG. 6 is a diagram showing the diffusion coefficient vs. potentialduring the oxidation (or charging) process of three different types offilm, in which the electrolyte solutions are all 0.3M LiClO₄ -PCsolution and the films as the positive electrodes are respectivelyPAn(-▪-), PAn/PVA(-♦-) and PAn/PVA/LiClO₄ (-▴-).

FIG. 7 is a diagram showing capacity vs. discharge/charge cycles of twobatteries, in which the positive electrode are respectivelyPAn/PVA/LiPF₆ (-▪-) and PAn/PVA/LiBF₄ (-♦-).

FIG. 8 is a diagram showing the capacity vs. discharge/charge cycles ofa battery containing PAn/PEO/LiClO₄ composite film.

DETAIL DESCRIPTION OF THE INVENTION

This invention provides an electroconductive polymer composite for usein secondary batteries as a positive electrode active material whichcomprises: 10-99 weight percent of a conjugated electroconductivepolymer and 90-1 weight percent of ionized polymeric electrolyte. Thelater comprises 10-90 weight percent of an ionic salt and 90-10 weightpercent of a polymer (referred to as the ionizable polymer) which canform an electrolyte material with the ionic salt. Preferably, thecontent of the conjugated electroconductive polymer is 1-5 times that ofthe ionizable polymer. And the content of the ionic salt is lower thanthe content of the ionizable polymer.

Suitable conjugated electroconductive polymers include polyanilines(PAn's), polypyrroles (PPy's) and polythiophenes (PT's), among which,polyaniline is preferred. A typical example of the polyanilines ispolyaniline. It can also be a copolymer formed by aniline and one ormore of the following three monomers: ##STR1## in which R is --OC_(n)H_(2n+1), --C_(n) H_(2n+1) or --C₆ H₅, n is an integer of 1 to 12. Othersuitable polyanilines are known in the industry, for example the onesdisclosed in U.S. Pat. No. 4,983,322. The disclosure of this patent isincorporated herein for reference.

The conjugated electroconductive polymer of this invention requires amolecular weight, in principle, high enough to form a film. Generallyspeaking, the number average molecular weight should be larger than1000.

Appropriate methods used in preparing the polyanilines include thechemical synthesis method and the electrochemical synthesis method.Steps of the former method include adding dropwisely 1M hydrochloricacid solution of ammonium persulfate (NH₄)₂ S₂ O₈ ! into a hydrochloricacid solution of aniline to proceed the oxidation polymerization.Several hours after the oxidation polymerization, HCl-doped polyanilinepowders with blue green color can be obtained. Using 1M ammonium water(NH₄ OH) to proceed de-doping, washing with water, and then drying, ade-doped polyaniline powder can be obtained. The electrochemical methodfor synthesis of polyaniline involves inserting a pair of electrodes inaniline acid solution and then applying an electric potential to proceedelectrochemical oxidation polymerization of aniline on the platinumanode.

The ionic salts suitable for use in this invention include (but are notlimited to) metal salts such as LiClO₄, LiBF₄, LiPF₆, LiSbF₆, LiBr,LiCl, Lil, LiAlCl₄, LiSCN, NaPF₆, NaSbF₆, NaAsF₆, NaClO₄, Nal, NaCl,KClO₄ and Zn(ClO₄)₂.

The ionizable polymers suitable for this invention include (but are notlimited to) polyvinyl alcohol and polyalkylene oxide and theircopolymers. Their number average molecular weight is larger than 1000.Preferably, the ionizable polymer is polyvinyl alcohol, polyethyleneoxide, polypropylene oxide, polybutylene oxide or copolymer of ethyleneoxide/propylene oxide.

An appropriate method of preparing the electroconductive polymercomposite comprises the steps of dissolving a desired ratio of theconjugated electroconductive polymer, the ionic salt and the ionizablepolymer in a common organic solvent and mixing the solution to form ahomogeneous mixture, and then drying and removing the solvent in themixture. Preferably, the mixture is cast on a flat substrate to form acoated layer and the solvent in the coated layer is removed to obtain anelectroconductive polymer composite film. The common organic solvent canbe, for example, 1-methyl-2-pyrrolidinone (NMP).

In the electroconductive polymer composite of this invention, the ionicsalt and the ionizable polymer form a polymeric electrolyte. And sincethe ionizable polymer and the conjugated electroconductive polymer areimmiscible to each other, the so-formed polymeric electrolyte isdispersed in the conjugated electroconductive polymer to form dispersedparticles with diameter of about 1 to 3 micrometer. Therefore, theconjugated electroconductive polymer and the polymeric electrolyte havea large contact area. Alternatively, the ionizable polymer can also bepresent as a block of the block copolymer with the conjugatedelectroconductive polymer. In the electroconductive polymer composite ofthis invention, the conjugated electroconductive polymer can store theenergy and the ionizable polymer provides ductility and also serves as areservoir for the ionic salt (or electrolyte). Therefore, when theelectroconductive polymer composites of this invention are used insecondary batteries as positive electrode, the electroconductive polymercomposites and the electrolytes of the secondary batteries have a largespecific contact area. Therefore, the ion flow rate is greatly increasedduring the process of battery charging and discharging. Furthermore, theductility provided by the ionizable polymer enable the electroconductivepolymer composites of this invention to be processed into a large areaflexible film.

A method of using the electroconductive polymer to prepare the positiveelectrode of a secondary battery comprises the steps of dissolving theabove three components in an appropriate solvent (such as1-methyl-2-pyrrolidinone), homogeneously mixing the solution, castingthe mixture on an appropriate metallic grid or plate (such as nickel,aluminum or platinum) and removing the solvent in the mixture to form afilm which adheres to the metal grid or plate. The film herein is thepositive electrode active material and the metallic grid or plate is thecurrent collector. Alternatively, the metallic grid or plate can bereplaced by a metallic thin film (such as nickel, aluminum or platinum)deposited on the surface of the film by use of thermal evaporation orsputtering.

A non-aqueous organic secondary battery can be made by using the abovepositive electrode. The secondary battery is composed mainly of: thepositive electrode, a negative electrode composed of a lithium, lithiumalloy, Li insertion compounds or other active metals such as Zn, Al, anda non-aqueous electrolyte solution.

The solvent used in the non-aqueous electrolyte solution includespropylene carbonate (PC) or its mixture with an other organic solventsuch as dimethoxyethane, lactones, or ethers. The reasons for choosingPC are that it has a high dielectric constant and dipole moment, andtherefore has a high solvation power, which results in a highperformance of the battery. The solvent was dried prior to use byremoving the minor content of water through the use of molecular sievefollowed with distillation twice. The dissolved electrolytes areselected from the metallic salts such as LiClO₄, LiBF₄, LiPF₆, LiSbF₆,Lil, LiBr, LiCl, LiAlCl₄, LiSCN, NaPF₆, NaSbF₆, NaAsF₆, NaClO₄, Nal,NaCl, KClO₄, Zn(ClO₄)₂, among which the commonly used electrolytes areLiClO₄, LiBF₄, LiPF₆ and LiAsF₆. The concentration of electrolyte isusually 0.2-3M. In the examples of this invention, the concentration isselected as 1.0M LiClO₄ -PC solution.

In order to avoid short circuits due to the contact of positive andnegative electrodes, a separator is added between the two electrodes inthe battery. The separator needs to have insulation capability andporosity so as to allow the passage of ions. The separator materialscommonly used are synthetic resins such as polypropylene, polyethyleneand fibrilar material.

The non-aqueous electrolyte solution in the non-aqueous organicsecondary battery can be substituted by a solid polymeric electrolyte togive an organic secondary battery containing a solid polymericelectrolyte. The solid polymeric electrolyte is an ionicelectroconductive polymer such as polyalkylene oxide or polyvinylalcohol with dissolved ionic salts therein.

The specific contact area between the electrolyte and theelectroconductive macromolecule electrode has a great influence onbattery performance. A battery electrode with a high specific contactarea can have increased powder density, charge capacity and energydensity and reduced charging time. Although the polyaniline film or itscomposite film has good mechanical properties, the film surface is quitecompact due to the plasticization by NMP. Therefore, the contact area ofthe film and the electrolyte solution is low. However, the compositefilm containing salt can improve this drawback because the PVA in thecomposite film contains dissolved salts. Therefore, the blending resultsin an increase in the specific contact area between the PAn andelectrolyte. As a result, the battery performance is increased. In orderto explain the merits of this invention, comparisons of the examples inthis invention and methods disclosed in the literature are given below.In the examples, mA is milliampere, V is volt, hr is hour, kg iskilogram, and W is watt.

EXAMPLE 1

200 ml of 1M HCl water solution, which contained 0.15 mole of ammoniumpersulfate ((NH₄)₂ S₂ O₈, Merck, GR), was prepared. The solution soprepared was added dropwisely into a 200 ml 1M HCl water solution whichcontained 0.1 mole of aniline (Merck, GR). The reaction then took placeunder an ice bath for several hours. Green precipitates were obtained.The green precipitates are polyaniline at the doped state. The dopedpolyaniline was then dispersed in 1.5M ammonium hydroxide aqueoussolution to undergo de-doping. The de-doped polyaniline powders werewashed with a large quantity of deionized water until the filtrate wasneutral and subsequently were dried under vacuum below 1 torr for 48hours. The undoped polyaniline powder and polyvinyl alcohol (PVA,Chang-Chun Petrochemical Co., Code: BP-17) powder (with averagemolecular weight of 7.5×10⁴) and lithium perchlorate (LiClO₄, Fluka, AG)at weight ratio of 1:1:0.6 were dissolved in NMP (Janssen, GC). Themixture was poured on a nickel grid and subjected to dynamic vacuumpumping below 1 torr at 50° C., in order to remove the solvent (NMP); aPAn/PVA/LiClO₄ composite film inserted with nickel grid was obtained. APAn/PVA/LiClO₄ composite film of 38 mg with a single face surface areaof 3 cm², thickness of 0.1 mm was used as the positive electrode of anorganic secondary battery. The nickel grid inserted in the film was usedas the current collector. Lithium metal was used as the negativeelectrode. 20 ml of 1.0M LiClO₄ -PC was used as electrolyte solution.The structure of the assembled organic secondary battery is shown inFIG. 1. The open circuit voltage (Voc) of the battery measured beforecharging/discharging was 3.04 V, and the short circuit current (Isc) was1.8 mA. The battery was then subjected to constant current (0.2 mA)charge/discharge cycles. The upper limit of the potential differencebetween the two electrodes during the charging was 4.1 V. The lowerlimit of the potential difference between the two electrodes during thedischarging was 1.5 V. The potential curve of the tenth charge/dischargecycle is shown in FIG. 2. From the variation of the potential vs.discharge time in FIG. 2, one can see that the time required for thepotential to drop from 3.7 V to 3.0 V was about 270 minutes which isquite close to the charge time of 300 minutes. This indicates that thebattery has a stable potential during use. After the tenth cycle, theopen circuit voltage was 3.70 V and the short circuit current was 27.8mA. The energy density based on the weight of the composite film was 85Whr/kg and based on the weight of polyaniline was 221 Whr/kg. Theaverage Coulomb efficiency of the battery was 91%.

EXAMPLE 2

Dissolved the undoped polyaniline as in example 1 and polyvinyl alcohol(PVA) in NMP at 1:1 weight ratio to give a homogeneous solution. Thesolution was then cast into film with an insertion of a nickel grid inaccordance with the procedures described in example 1. Please note thatthe film does not contain electrolyte. A PAn/PVA composite film of 24.2mg with a single face surface area of 2.8 cm², thickness of 0.07 mm wasused as the positive electrode. The negative electrode and theelectrolyte solution were the same as in example 1. The nickel gridinserted in the film was used as the current collector. Beforecharge/discharge, the open circuit voltage of the battery was 2.75 V. Asin example 1, the battery was also subjected to constant current (0.2mA) charge/discharge cycles. The upper limit of charge was 4.1 V, andthe lower limit of discharge was 1.5 V. The open circuit voltage after60 cycles of charge/discharge was 3.70 V and the short circuit current(Isc) was 2.1 mA. The energy density based on weight of the PAn/PVAcomposite film was 26 Whr/kg and based on the weight of polyaniline was52 Whr/kg. The average Coulomb efficiency of the battery was 97%.

EXAMPLE 3

Dissolved undoped polyaniline powder as in example 1 in NMP to give ahomogenous solution. The solution was then cast into film with aninsertion of a nickel grid in accordance with the procedures describedin example 1. Please note that the film does not contain electrolyte. APAn film of 26 mg with a single face surface area of 2.8 cm², thicknessof about 0.07 mm was used as the positive electrode. The nickel grid wasused as the current collector. The negative electrode and theelectrolyte solution were the same as in example 1. Beforecharge/discharge, the open circuit voltage of the battery was 2.90 V andthe short circuit current was 0.7 mA. As in example 1, 0.2 mA constantcurrent was used to proceed the charge/discharge cycles. The upper limitof charge was 4.1 V and the lower limit of discharge was 1.5 V. The opencircuit voltage after 30 cycles of charge/discharge was 3.73 V and theshort circuit current (Isc) was 5.9 mA. The energy density was 65Whr/kg. The average Coulomb efficiency of the battery was 89%.

Table 1 lists the performances of the above three examples after tencycles of charge/discharge. From the table, one can learn that whenPAn/PVA/LiClO₄ composite film was used as the positive electrode, thebattery has the highest energy density and charge capacity. This is dueto that the contact area between the PAn and the electrolyte is verylarge as can be seen from the higher short circuit current. From theexperimental data of charge/discharge, the energy densities of the aboveexamples can be calculated, being 85 Whr/kg, 26 Whr/kg, 65 Whr/kg,respectively. The energy densities corresponding to the weight of thepolyaniline are 221 Whr/kg, 52 Whr/kg, and 65 Whr/kg, respectively,among which the PAn/PVA/LiClO₄ composite film has the highest value. Incomparison with lead acid battery, the energy density of composite filmbattery is about six times higher. The decay of open circuit voltages ofthe three batteries vs. time are shown in FIG. 3. As can be seen, thethree batteries have similar stability.

The charge capacities and energy densities of the above three examplesare relatively low. This is because the polyaniline film used as thepositive electrode is too thick or the surface area of the currentcollector is too small. This causes that only the locations close to thecurrent collector have charge/discharge reaction and the rest of thepolyaniline remain inert. Therefore, the overall charge capacity andenergy density are decreased. In order to improve this drawback, theinventors have used a platinum foil as the current collector to replacethe nickel grid and reduced the composite film thickness. Theircharge/discharge characteristics are explained in the following fourexamples.

                                      TABLE 1    __________________________________________________________________________    Battery Performances of Examples 1, 2, 3    (After Tenth Charge/Discharge Cycles)                        Open                            Short    Energy                        Circuit                            Circuit                                Energy                                     Density    Battery        Positive             Negative                  Electrolyte                        Voltage                            Current                                Density                                     (Whr/kg)                                          Capacity    NO  Electrode             Electrode                  solution                        (V) (mA)                                (Whr/kg)                                     @    (Ahr/kg)    __________________________________________________________________________    1   PAn/PVA/             Li   1.0M  3.70                            27.8                                85   221  25        LiClO.sub.4                  LiClO.sub.4 --PC        on Ni        3.0 cm.sup.2        38 mg    2   PAn/PVA             Li   1.0M  3.70                             2.1                                26    52   8        on Ni     LiClO.sub.4 --PC        2.8 cm.sup.2        24.2 mg    3   PAn  Li   1.0M  3.73                             5.9                                65    65  20        on Ni     LiClO.sub.4 --PC        2.8 cm.sup.2        26 mg    #   PbO.sub.2             Pb   H.sub.2 SO.sub.4                        2.0 --  30-40                                     --   --                  aq-    __________________________________________________________________________     @ Based on weight of polyaniline.     # Leadacid battery

EXAMPLE 4

According to the procedures of preparation in example 1, a solution ofPAn/PVA/LiClO₄ at weight ratio of 1:1:0.6 in NMP was prepared. Thesolution was then cast on metallic foil (such as platinum, stainlesssteel foil, aluminum foil) and subjected to dynamic vacuum pumping below1 torr at 50° C., and a PAn/PVA/LiClO₄ composite film was obtained. Thecomposite film of 1.0 mg with a single face surface area of 3.0 cm² andthickness of about 0.003 mm was used as the positive electrode. Themetallic foil was used as the current collector. The negative electrodeand the electrolyte solution were the same as in example 1. As inexample 1, 0.2 mA current was used to proceed the constant currentcharge/discharge cycles. The upper limit of charge was 4.1 V and thelower limit of discharge was 2.0 V. The open circuit voltage after 240cycles of charge/discharge was 3.80 V and the short circuit current(Isc) was 28 mA. The energy density based on the weight of thePAn/PVA/LiClO₄ composite film was 125 Whr/kg and that based on theweight of polyaniline was 325 Whr/kg. The variation of charge capacitywith cycle number in FIG. 4 shows that the battery has a stable chargecapacity.

EXAMPLE 5

The weight ratio of PAn/PVA/LiClO₄ composite film in example 4 waschanged to 2:1:0.5. The composite film of 0.5 mg having a single facesurface area of 2.6 cm² and thickness of about 0.002 mm was used as thepositive electrode. The other experiment conditions were the same as inexample 4. The open circuit voltage after 200 cycles of charge/dischargewas 3.80 V and the short circuit current (Isc) was 28 mA. The energydensity based on the weight of the PAn/PVA/LiClO₄ composite film was 208Whr/kg and based on the weight of polyaniline was 364 Whr/kg. Thevariation of charge capacity with cycle number in FIG. 4 shows that thebattery has a stable charge capacity.

EXAMPLE 6

The weight ratio of PAn/PVA/LiClO₄ composite film in example 4 waschanged to 3:1:0.6. The composite film of 0.4 mg having a single facesurface area of 2.6 cm² and thickness of about 0.0015 mm was used as thepositive electrode. The other experiment conditions were the same as inexample 4. The open circuit voltage after 240 cycles of charge/dischargewas 3.75 V and the short circuit current (Isc) was 28 mA. The energydensity based on the weight of the PAn/PVA/LiClO₄ composite film was 263Whr/kg and based on the weight of the polyaniline was 374 Whr/kg. Thevariation of charge capacity with cycle number shown in FIG. 4 showsthat the battery has a stable charge capacity.

EXAMPLE 7

The PAn solution of example 3 was cast on a metallic foil (such asplatinum, stainless steel foil, aluminum foil), and then subjected todynamic vacuum pumping below 1 torr at 50° C. to obtain a PAn film. Thefilm of 0.9 mg with a single face surface area of 2.2 cm² and thicknessof about 0.002 mm was used as the positive electrode. The otherexperiment conditions were the same as in example 4. The open circuitvoltage after 240 cycles of charge/discharge was 3.78 V and the shortcircuit current (Isc) was 25 mA. The energy density was 110 Whr/kg. Thevariation of charge capacity with cycle number FIG. 4 shows that thebattery has a stable charge capacity.

EXAMPLE 8

After the battery in example 5 has been set aside for four months, theopen circuit voltage was 3.2 V. After charge/discharge experiments, theenergy density of the battery based on the weight of the PAn/PVA/LiClO₄composite film was 163 Whr/kg and based on the weight of polyaniline was289 Whr/kg. In comparison with example 5, the open circuit voltage andenergy density of the battery has decreased by only 15% and 21%respectively. The reason for such decay is that the lithium reacted witha tiny amount of water in the system (this can be observed from that thelithium surface has turned to black), causing the decreased performanceof the battery. This problem can be avoided by removing the watercompletely and by prevention from the leakage of air into the battery.

The performances of the batteries in examples 4 to 7 after 15 cycles ofcharge/discharge are listed in Table 2. As can be seen, when aPAn/PVA/LiClO₄ composite film was used as the positive electrode, theenergy density, open circuit voltage and short circuit current werehigher than those of the battery with PAn film. FIG. 5 shows themorphologies of the PAn film cast from PAn solution in NMP, and thePAn/PVA/LiClO₄ composite film with a weight ratio of 2:1:0.6. AS can beseen, the surface of PAn is quite compact and featureless and that ofthe composite film less experienced a phase separation with thedispersed phase being a complex of PVA and salt and the continuous phasebeing PAn. Since the PVA phase contains the electrolyte, the specificcontact area of PAn and electrolyte is very large. During charging, theanions could directly diffuse from the PVA phase into the PAn phase,which allows an improvement of the drawback due to a small specific areaof PAn film. Using the spectro-electrochemical method, the diffusioncoefficient of the ions in the polyaniline film and the PAn/PVA andPAn/PVA/LiClO₄ composite films were measured, the results are shown inFIG. 6. From FIG. 6, one can see that the composite film ofPAn/PVA/LiClO₄ has the highest ion diffusion coefficient. That is thebattery has the highest charge/discharge rate when PAn/PVA/LiClO₄ filmwas used as a positive electrode. The composition of the composite filmalso has great influence on the performance of the battery. ThePAn/PVA/LiClO₄ composite film with a weight ratio of 3:1:0.6 has thehighest energy density; that with a weight ratio of 2:1:0.5 is next; andthat with a weight ratio of 1:1:0.6 is the smallest. Among these threecomposites, when the PAn content is higher, the battery has betterperformance. In comparison with the lead battery, the battery with thecomposite film has an energy density ten times higher.

                  TABLE 2    ______________________________________    Battery Performances of Examples 4, 5, 6, 7    (After Fifteenth Charge/Discharge Cycle)                  Open    Short        Energy    Bat-          Circuit Circuit                                Energy Density    tery Positive Voltage Current                                Density                                       (Whr/kg)    No   Electrode                  (V)     (mA)  (Whr/kg)                                       @      Capacity    ______________________________________    4    PAn/PVA/ 3.80    28    125    325    39         LiClO.sub.4         (1:1:0.6)         2.5 cm.sup.2         0.7 mg    5    PAn/PVA/ 3.80    28    208    364    64         LiClO.sub.4         (2:1:0.5)         2.6 cm.sup.2         0.5 mg    6    PAn/PVA/ 3.80    28    263    374    80         LiClO.sub.4         (3:1:0.6)         2.1 cm.sup.2         0.4 mg    7    PAn      3.78    25    110    --     36         2.2 cm.sup.2         0.9 mg    ______________________________________     @ Based on weight of polyaniline.

EXAMPLE 9

According to the procedures of preparation in example 1, a ion ofPAn/PVA/LiBF₄ at a weight ratio of 1:1:0.6 in NMP was prepared. Thesolution was cast on metallic foil (such as platinum, stainless steelfoil, aluminum foil) and subjected to dynamic vacuum pumping below 1torr at 50° C., a PAn/PVA/LiBF₄ composite film was obtained. Thecomposite film of 0.35 mg with a single face surface area of 2.9 cm² wasused as the positive electrode. The metallic foil was used as thecurrent collector. The negative electrode and the electrolyte solutionwere the same as in example 1. As in example 1, 0.2 mA current was usedto proceed the constant current charge/discharge cycles. The upper limitof charge was 4.1 V and the lower limit of discharge was 2.0 V. The opencircuit voltage after 250 cycles of charge/discharge was 3.85 V and theshort circuit current (Isc) was 9.5 mA. The energy density based onweight of the PAn/PVA/LiBF₄ composite film was 71 Whrlkg and that basedon the weight of polyaniline was 185 Whr/kg. The variation of the chargecapacity with the cycle number in FIG. 7 shows that the battery has astable charge capacity.

EXAMPLE 10

According to the procedures of preparation in example 1, a solution ofPAn/PVA/LiPF₆ at weight ratio of 1:1:0.6 in NMP was prepared. Thesolution was then cast on metal foil (such as platinum, stainless steelfoil, aluminum foil) and subjected to dynamic vacuum pumping below 1torr at 50° C., a PAn/PVA/LiPF₆ composite film was obtained. Thecomposite film of 0.45 mg with a single side surface area of 3.12 cm²was used the positive electrode. The metallic foil was used as thecurrent collector. The negative electrode and the electrolyte solutionwere the same as in example 1. As in example 1, a 0.2 mA current wasused to proceed the constant current charge/discharge cycles. The upperlimit of charge was 4.1 V and the lower limit of discharge was 2.0 V.The open circuit voltage after 250 cycles of charge/discharge was 3.80 Vand the short circuit current (Isc) was 10 mA. The energy density basedon the weight of the PAn/PVA/LiPF₆ composite film was 83 Whr/kg and thatbased on the weight of polyaniline was 216 Whr/kg. The variation ofcharge capacity with the cycle number in FIG. 7 shows that the batteryhas a stable charge capacity.

EXAMPLE 11

According to the procedures of preparation in example 1, a solution ofPAn/PEO/LiClO₄ at a weight ratio of 1:1:0.6 in NMP was prepared. Thepolyethylene oxide (PEO, Polysciences, Inc.) used here had a molecularweight of 4×10⁶. The solution was cast on metallic foil (such asplatinum, stainless steel foil, aluminum foil) and subjected to dynamicvacuum pumping below torr at 50° C., a PAn/PEO/LiClO₄ composite film wasobtained. The composite film of 0.5 mg with a single side surface areaof 2.9 cm² was used as the positive electrode. The metallic foil wasused as the current collector. The negative electrode and theelectrolyte solution were the same as in example 1. As in example 1, 0.2mA current was used to proceed the constant current charge/dischargecycles. The upper limit of charge was 4.1 V and the lower limit ofdischarge was 2.0 V. The open circuit voltage after 300 cycles ofcharge/discharge was 3.60 V and the short circuit current (Isc) was 15mA. The energy density based on the weight of the PAn/PEO/LiClO₄composite film was 180 Whr/kg and that based on the weight ofpolyaniline was 466 Whr/kg. The variation of charge capacity with cyclenumber in FIG. 8 shows that the battery has a less stable chargecapacity than the battery with PAn/PVA/LiClO₄ composite film.

The performances of the batteries in examples 9 to 11 after 15 cycles ofcharge/discharge are listed in Table 3. As can be seen from Table 2 andTable 3, when PAn/PVA/LiClO₄ composite film was used as the positiveelectrode of the battery, the energy density and short circuit currentthereof were higher than those of the battery with PAn/PVA/LiBF₄ andPAn/PVA/LiPF₆ composite films. The main reasons are that the ion radiusof ClO₄ - is smaller than that of PF₆ -, and the former has higheroxidation power than the latter. This enables ClO₄ - to provide thelargest doping capacity and, as a result, to enhance the overallperformance of the battery.

From the experimental results above, the organic secondary battery withthe polyaniline composite film of this invention as the positiveelectrode has higher charge capacity, energy density and power density.Furthermore, due to the flexibility of this polymeric electrode, it canbe used to produce a large area flexible organic secondary battery andfilm battery.

                  TABLE 3    ______________________________________    Battery Performances of Examples 9, 10, 11    (After Fifteenth Charge/Discharge Cycle)                  Open    Short        Energy    Bat-          Circuit Circuit                                Energy Density    tery Positive Voltage Current                                Density                                       (Whr/kg)                                              Capacity    No   Electrode                  (V)     (mA)  (Whr/kg)                                       @      (Ahr/kg)    ______________________________________     9   PAn/PVA/ 3.85     9.5   46    120    14         LiBF.sub.4         (1:1:0.6)         2.9 cm.sup.2         0.35 mg    10   PAn/PVA/ 3.80    10.0   79    206    25         LiPF.sub.6         (1:1:0.6)         3.1 cm.sup.2         0.45 mg    11   PAn/PEO/ 3.60    15.0  180    466    56         LiClO.sub.4         (1:1:0.6)         2.1 cm.sup.2         0.5 mg    ______________________________________     @ Based on weight of polyaniline.

What is claimed is:
 1. An electroconductive polymer composition for useas a positive electrode active material in secondary batteries,comprising 10-99 weight percent of a conjugated electroconductivepolymer, and 90-1 weight percent of an ionized polymeric electrolytemixture;wherein the ionized polymeric electrolyte mixture comprises10-90 weight percent of an ionic salt and 90-10 weight percent of anionizable polymer the amount of the conjugated electroconductive polymeris 1-5 times of the amount of said ionizable polymer and the amount ofthe ionic salt is smaller than that of the ionizable polymer, and theionizable polymer is dispersed in the conjugated electroconductivepolymer having particle diameters of 1-3 micrometers.
 2. Theelectroconductive polymer composition of claim 1 wherein the ionizablepolymer and the conjugated electroconductive polymer form a blockcopolymer.
 3. The electroconductive polymer composition of claim 1wherein the conjugated electroconductive polymer is selected from thegroup consisting of polyanilines, polypyrroles, and polythiophenes. 4.The electroconductive polymer composition of claim 3 wherein theconjugated electroconductive polymer is polyanilines.
 5. Theelectroconductive polymer composition of claim 4 wherein thepolyanilines are polyaniline or a copolymer formed by aniline and one ormore of the following three monomers ##STR2## in which R is --OC_(n)H_(2n+1),--C_(n) H_(2n+1), or --C₆ H₅, n is an integer of 1 to 12, andthe polyaniline have a number average molecular weight larger than 1000.6. The electroconductive polymer composition of claim 1 wherein theionic salt is a metallic salt selected from the group consisting ofLiClO₄, LiBF₄, LiPF₆, LiSbF₆, LiBr, LiCl, Lil, LiAlCl₄, LiSCN, NaPF₆,NaSbF6, NaAsF6, NaClO₄, Nal, NaCl, KClO₄, and Zn(ClO₄)₂.
 7. Theelectroconductive polymer composition of claim 6 wherein the ionic saltis LiClO₄, LiBF₄ or LiPF₆.
 8. The electroconductive polymer compositionof claim 1 wherein the ionizable polymer is polyvinyl alcohol,polyalkylene oxide or copolymers of vinyl alcohol and of elkylene oxide,and the number average molecular weight of the ionizable polymer islarger than
 1000. 9. The electroconductive polymer composition of claim8 wherein the ionizable polymer is polyvinyl alcohol, polyethyleneoxide, polypropylene oxide, polybutylene oxide or a copolymer ofethylene oxide/propylene oxide.